Bilam ha'rasha was a novi, but at the same time he is always referred to as Bilam ha'rasha - the evil one. One may wonder - was his external appearance that of a novi or that of a rasha?
The mishna in Pirkei Avos (5:19) describes the contrast between the talmidim of Avrohom Avinu and the talmidim of Bilam ha'rasha. The pesukim that indicate the difference are pesukim spoken by Bilam, not by his talmidim. Why doesn't the mishnah draw a contrast between Avrohom Avinu and Bilam himself?
Some of the commentaries point out that when one would look at Bilam you could be fooled to believe that he himself is the same type of person as Avrohom Avinu. Because he was a novi he dressed the part, acted the part, and spoke the part. You could only tell the difference between the two when you look at their talmidim.
According to the haftorah of Parshas Vayishlach the stranger who mugged Yaakov Avinu in the middle of the night was an angel. The midrash explains that he was soro shel Eisav - Eisav's angel. The gemorah (Chullin 91a) has a discussion regarding what this angel looked like. One opinion is that his appearance was similar to that of a talmid chachom. Looks are often deceiving - soro shel Eisav can dress up like a talmid chacham. It is known that the Chofetz Chaim used to dress like a plain ba'al ha'bayis. In fact there were those that referred to him as the "ba'al ha'bayis". But we know from the influence that he had on so many of his followers that he was so much more than a plain ba'al ha'bayis. Unfortunately there are many rabbonim who dress the part, act the part, and speak the part, but when we look at their followers we realize that in their inner core there is something seriously lacking.
In a famous teshuva written by the Maharshal he complains about the fact that in his generation there were many honest-to-goodness talmidei chachomim who did not have the minhag to wear a yarmulke all day long and the public would frown upon them. But any Torah scholar who would wear a yarmulke would be honored and respected even if his Torah knowledge and yiras shomayim were not up to par. Looks are often deceiving. The mishna (Pirkei Avos 4:20) warns us, "al tistakel b'kankan eleh b'mah sh'yesh bo - one should not judge a person merely based on externalities." When one is deciding whom to follow as his rebbe, in fulfillment of the instructions in the mishna (Pirkei Avos 1:6), "asei l'cho rav", one must judge whether the rabbi in question is the right person in his inner core based on the rabbi's talmidim.